This invention relates to the field of pumps for handling liquids, and particularly to water pumps for use with steam cleaning apparatus at locations where a supply of water under pressure is not available. For such uses, there is need for a small, heavy duty water pump which is simple in construction and adjustment and which operates for long periods without maintenance.
A pump having most of these characteristics is taught in Gearhart U.S. Pat. No. 3,046,070, which discloses a piston reciprocable in a cylinder. The piston comprises an enlarged head and a stem of reduced diameter carrying a packing which is compressed against the head and thus is forced into slidingly sealing engagement with the cylinder by means threadedly engaging the stem and fixed by jam nuts.
This structure has the imperfection that it is very difficult to adjust the compression of the packing exactly as it should be. If the packing is too tight, excessive friction between it and the cylinder results in destructive heat which burns out the packing. If the packing is too loose, leakage of water past the packing becomes significant.